Dew point sensitive computer cooling system

ABSTRACT

A computer cooling system has a mixing valve which supplies coolant to the computer and receives hot return coolant from the computer and also chilled return coolant from a chiller intermediate the computer and the mixing valve. The mixing valve mixes the hot return coolant with the chilled return coolant to adjust the cooling system temperature. Control circuitry senses, or estimates, the dew point temperature of the computer room environment, compares it with the cooling system temperature, and adjusts the mixing valve to maintain the cooling system temperature a few degrees above the dew point temperature. A condensation sensor comprises of a light emitting diode (LED), reflective tape applied about a cooling system supply conduit, and a phototransistor is disclosed. Light from the LED is fully reflected by the reflective tape to the phototransistor in dry conditions, but only partially reflected when condensation forms on the tape. The phototransistor output drops when condensation impedes the reflectability of the tape resulting in only partial reflection of the light and this drop in the phototransistor output is sensed by circuitry associated therewith to shut down the coolant pump and the computer system.

This is a division of application Ser. No. 471,953 filed Mar. 3, 1983.

BACKGROUND

The invention relates to cooling systems for computers, andparticularly, to a cooling system designed to prevent condensationwithin the computer.

It has been customary among at least some computer manufacturers togenerally assume a 56° F. dew point (or other designated temperature) inthe computer room environment, and to shut down the system when theroom, or individual computer cabinets, reach 56° or 57°. Accordingly,users of these computer systems have been required to maintain thecomputer rooms at least above the 56° F. estimated dew point temperature24 hours a day, 7 days a week.

With the increasing costs of energy, however, many users want to relaxthe computer room environmental controls on weekends and at other times,and also to lower building temperatures in winter and relax airconditioning in the summer to reduce their escalating heating andcooling costs.

The problem presented has been to enable users to relax theirenvironmental computer room controls while still preventing condensationwithin the computers.

SUMMARY

The present invention solves the problems presented by the prior systemsby providing a cooling system which monitors dew point temperature (orestimates it based on temperature and relative humidity readings) andmaintains the cooling system temperature a few degrees above the dewpoint temperature.

Accordingly, when the dew point temperature drops, the temperature ofthe computer room can also be reduced to save energy and allow thecomputer to run cooler and more efficiently. In addition to savingenergy, electronic chips run more efficiently at cooler temperatures andalso their useful lives are increased by operating at coolertemperatures. Conversely, when the dew point temperature increases, thetemperature of the coolant system is increased to avoid the possibilityof condensation within the computer.

A condensation sensor is disclosed which senses the formation ofcondensation on the cooling system supply conduits and shuts the coolingsystem off in response thereto to prevent further condensation withinthe computer.

It is therefore an object of the present invention to provide animproved cooling system for a computer.

It is another object to provide a cooling system which senses orestimates the computer room environment dew point temperature andmaintains the cooling system temperature at a few degrees above the dewpoint temperature.

Yet another object is to provide a cooling system which includes acondensation sensor which senses the presence of condensation on thecooling system conduits and shuts down the system in response thereto.

Still another object is to provide a computer cooling system wherein thecomputer room environment relative humidity and temperature values areused to estimate dew point and to maintain the cooling system a fewdegrees above the estimated dew point temperature.

Still another object is to provide a computer cooling system wherein thecooling system temperature value is compared with a dew pointtemperature value and an error signal is generated to open or close thecooling system mixing valve to mix in more or less chilled return wateras necessary to maintain the cooling system temperature a few degreesabove dew point.

Still another object is to provide a cooling system wherein the openingor closing of the mixing valve to vary system temperature in response todew point system temperature comparisons is damped to prevent the systemfrom overshooting.

Still another object is to provide a computer cooling system which isswitchable between an automatic mode and a manual mode, and wherein inthe manual mode an adjustable temperature setting mechanism is used toset the system temperature, whereas in the automatic mode the sametemperature setting mechanism can be used to set the minimum coolingsystem temperature.

Still another object is to provide a condensation sensor which employs alight source operably disposed with respect to a reflective surface anda light sensing device so that light from the source is fully reflectedto the sensing device in dry conditions, but only partially reflectedwhen condensation forms on the reflective surface, and wherein thesensor shuts down the system where the light is only partially reflecteddue to condensation.

These and other objects, advantages and novel features of the inventionwill become apparent from the following detailed description of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of the invention.

FIG. 2 is a block diagram of the control circuitry of the invention.

FIG. 3 is a circuit diagram of the control circuitry.

FIG. 4 is an elevational view of the condensation sensor of the presentinvention.

FIG. 5 is a circuit diagram of the condensation sensor circuitry of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention comprises a cooling system for a computer which monitorsthe dew point temperature of the computer room environment and maintainsthe cooling system temperature a few degrees above the dew pointtemperature. The invention also includes a condensation sensor employedin the cooling system to shut the system down whenever condensationforms within the system.

In FIG. 1, the computer sections cooled by the cooling system 1 aredesignated by the numerals 5, 7, and 9. The system 1 includes a dualwinding mixing valve motor 13 which drives a three-way mixing valve 17in the open or closed direction by means of a motor shaft 15. Coolant issupplied by mixing valve 17 to the computer sections 5, 7, and 9 viamain coolant supply conduit 19, supply manifold 21 and section supplyconduits 23, 25, and 27. The coolant cools the computer sections 5, 7,and 9 and then exits the sections as hot coolant via section returnconduits 31, 33, and 35. The hot coolant is collected in a hot coolantreturn manifold 37 and then passes into main coolant return conduit 39.Return conduit 39 splits into a first branch 41 and a second branch 43.First branch 41 supplies hot return coolant to mixing valve 17. Secondbranch 43 sends hot coolant through the system chiller 47 via a heatexchange coil 49. The hot coolant gives up its heat in the coil 49 tothe circulating chilled building water in the chiller 47 and then passesto mixing valve 17 via conduit 51 as chilled return coolant. Mixingvalve 17 is controlled by motor 13 to mix the proper amount of chilledreturn coolant with hot return coolant to provide the proper temperaturecoolant to supply conduit 19. For example, when motor 13 drives mixingvalve 17 fully open, hot return conduit 41 is shut off and only chilledcoolant is supplied to conduit 19. On the other hand, when motor 13drives mixing valve 17 fully closed, chilled return conduit 51 is shutoff and only hot coolant through conduit 41 is supplied to conduit 19.Intermediate to these fully closed and fully open positions, the valve17 mixes the hot return coolant with the chilled return coolant toachieve the proper supply coolant temperature.

According to the invention, a control circuit 61 is provided whichdetermines or estimates the dew point temperature of the computer roomenvironment and compares that temperature to the temperature of thecoolant at the coolant supply manifold 21. Based on this comparison,control circuitry 61 sends appropriate signals to mixing valve motor 13to adjust the valve 17 as necessary to reduce or increase thetemperature of the coolant so that the coolant system temperature atsupply manifold 21 is maintained a few degrees above the dew pointtemperature. The coolant system temperature is sensed at the coolantsupply manifold 21 by a 100K thermistor (not shown). The manifold 21 isbelieved to be the coldest part of the cooling system. By maintainingthe coldest part of the cooling system a few degrees above dew point,condensation within the remainder of the system is avoided.

FIG. 1 shows system temperature input 65 to control circuitry 61 fromthe manifold 21. In addition, a room temperature input 67 and a relativehumidity input 69 are shown. As will be explained more fully later on inthe description, in the presently preferred embodiment of the invention,dew point temperature is estimated from these temperature and humidityinputs 67 and 69. It is to be understood however that the invention alsocovers a system wherein the dew point temperature is determined directlyby a commercially available meter (such as is provided by the GeneralEastern Instruments Corporation, Watertown, Mass.) and then inputdirectly into the control circuitry 21 for comparison with the coolingsystem temperature.

Reference is now made to FIG. 2 wherein a functional block diagram ofthe basic control circuitry 61 is disclosed. The cooling systemtemperature input 65 as well as the room temperature input 67 andrelative humidity input 69 are input to controlled circuitry 61 from theleft in FIG. 2. Control circuitry 61 has two modes of operation: anautomatic mode and a manual mode. In the automatic mode switches S1 andS2 are rotated counterclockwise to close contacts 74 and 82. This is theautomatic position. In the manual mode, switches S1 and S2 are rotatedclockwise to close contacts 76 and 84, respectively. This is the manualposition. Control circuit 61 will first be described as it operates inthe automatic mode and will then be described as it operates in themanual mode.

In the automatic mode, the room temperature input 67 and relativehumidity input 69 are converted by dew point calculating circuit 71 toan estimate of the dew point temperature based on an emperically derivedformula which will be later disclosed. This estimated dew pointtemperature is input to comparator circuit 75 via output 73. Comparatorcircuit 75 compares the dew point temperature input 75 with the systemtemperature input 65 and determines a temperature differential valuewhich it sends to the error producing amplifier 79 via output 77. Areference value, here 5° F. is also input into error producing amplifier79 via input 81 and contacts 82 of switch S2. The amplifier 79 comparesthe temperature differential value 77 with the reference value 81. Ifthe temperature differential is more than the reference value, thenamplifier 79 outputs a first type of error signal indicating that thesystem temperature is more than 5° F. above the dew point temperature.If, on the other hand, temperature differential 77 is less thanreference value 81, amplifier 71 will output a second type of errorsignal indicating that the system temperature is less than 5° F. abovedew point. These first or second type error signals are output to motorcontrol switch 85 which provides a digital high-level signal to chilllogic 89 via output 87 in the case of a first type error signal, oralternatively, a digital high-level signal to the heat logic 93 viaoutput 91 in the case of a second type error signal. Ignoring for themoment the optional inputs 95 and 97 to chill logic 89, and the optionalinput 99 to heat logic 93, chill logic 89 turns on motor control circuit103 via output 101 in response to a high-level signal on input 87. Motorcontrol circuit 103, in turn, drives the mixing valve motor via output105 in the open direction to mix in more chilled water and reduce thesystem coolant temperature for so long as it is enabled by chill logic89. Conversely, heat logic 93 turns on motor control 109 via output 107in response to a high-level signal on input 91. Motor control 109, inturn, drives mixing drive motor 13 in the close direction via output 111for so long as it is enabled by heat logic 93 to mix in more hot returncoolant to raise the system coolant temperature. Hence, in the simplestform of the system, where the system temperature is more than 5° greaterthan the dewpoint temperature, control circuitry 61 opens mixing valve17 to lower the system cooling temperature; and where the coolanttemperature is less than 5° above dew point, the circuitry 61 closesmixing valve 17 to heat up the system coolant temperature. Accordingly,circuitry 61 continuously maintains the system coolant temperature atapproximately 5° F. above the dew point temperature.

Having described the simplest form of the control circuitry 61 as itfunctions in the automatic mode, certain optional enhancements of thesystem will now be described. As shown in FIG. 2, the circuitry 61includes a damping circuit 121. The purpose of damping circuit 121 is todamp system response to minimize the oscillation of the system about the5° F. above dew point reference temperature. Damping circuit 121includes a timing capacitor (later described) which is charged by input119 as soon as the motor 13 begins to turn in either the open or theclosed direction. Once the motor has continuously turned in either theopen or closed direction for a sufficient period of time to charge thetiming capacitor, damping circuit 121 outputs a low-level signal viaeither its output 97 or 99 (97 if the motor has been turning in the opendirection, 99 if the motor has been turning in the closed direction) tochill logic 89 or heat logic 93 to shut off the motor 13. The motor 13is then disabled until the timing capacitor discharges. Once thecapacitor has discharged, a high-level enabling signal is againpresented by damping circuit 121 to the chill logic 89 or heat logic 93via conductors 97 or 99, respectively. Damping circuit 121 thus causesthe mixing valve 13 to open or close in a stepped manner to give thecooling system time to respond to the changing mixture of chilled andhot return coolant before completely opening or closing the mixingvalve. This dampening of the mixing valve motion prevents the systemfrom overshooting its mark and continually hunting about the 5° F. abovedew point reference temperature.

The other input to chill logic 89 which was formerly ignored was input95. A minimum temperature setting circuit 133 includes a dial and scale(not shown) which permits the user to set a minimum temperature valuefor the system. This minimum temperature value is output to a minimumtemperature comparator 131 via output 135 where it is compared with thecooling system temperature value 65. So long as system temperature 65 isabove the minimum temperature setting 135, comparator 131 outputs ahigh-level enabling signal via its output 95 to chill logic 89. If,however, the system temperture 65 falls below the minimum temperaturesetting 135, comparator 131 outputs a low-level signal which disableschill logic 89 until the system temperature has risen above the minimumtemperature setting.

Having described the basic and enhanced versions of the automatic mode,the operation of circuit 61 in the manual mode is now described.

As noted previously, in the manual mode switches S1 and S2 are rotatedcounterclockwise in FIG. 2 to close contact 76 and 84 and open contacts74 and 82. With contact 76 closed, the output 135 of temperature settingcircuit 133 passes through the contact 76 and is input to comparatorcircuit 75 where it is compared with the system temperature 65.Comparator circuit 75 determines the temperature differential betweensetting 135 and system temperature 65 and outputs this differentialvalue to error producing circuit 79. Since contacts 84 are now closed byS2, a ground potential signal is input to the error producing circuit79. Accordingly, the temperature differential value output by comparatorcircuit 75 will be compared to ground potential. If the systemtemperature is greater than the temperature setting at circuit 133, thana positive differential value will be compared with ground and a firsttype error signal will be output enabling the chill logic (assuming thetwo conditions previously discussed are met) and opening the mixturevalve to reduce system temperature. If, however, system temperature 65is below the set temperature value 135, then comparator circuitry 75will output a negative differential value which will be compared withground and error producing circuit 79 to generate a second type errorsignal. The second type error signal will enable the heat logic(assuming the condition previously mentioned is met) to close down themixing valve to increase system temperature.

Hence, the temperature value set at the circuitry 135 is utilized to setthe minimum system temperature in the automatic mode and used to set thesystem coolant temperature at the supply manifold 21 in the manual mode.

Having described both the automatic and manual modes, control circuitry61 will now be explained in more detail with reference to the circuitdiagram shown in FIG. 3.

The room temperature "T" and the relative humidity "RH" inputs 67 and69, which are input from the left in FIG. 3, are obtained from a GeneralEastern Model 411 RH and Temperature Sensor. The temperature input T isscaled from 0 volts to 5 volts for 0° F. to 100° F. Thus, input T, orV_(T), is scaled at 0.05 volts/°F. over the range of interest (50°F.-90° F.). The RH input is scaled from 0 volts to 5 volts for 0% to100% humidity. Hence, the input RH, or V_(RH), is scaled for 0.05 V/%RHover the range of interest (30%-70%). The V_(T) value passes through a10K resistor 141 to node 147, while the V_(RH) value passes through a24K resistor 143 to node 147. A minus 4.5 volt reference value alsopasses through a 24K resistor 145 to node 147. Given this resistornetwork and these inputs, the voltage at node 147, or the dew point tempvoltage V_(DPT), is given by the formula:

    V.sub.DPT =V.sub.T +(V.sub.RH -4.5)/.sub.12.4

The above formula has been empirically derived by the applicants hereinas an approximation of dew point temperature for the typical range oftemperature and relative humidity values which a computer roomenvironment will be likely to experience. The formula estimates thecorresponding dew point readings for the temperature and humidity valuesselected as determined from a psychrometric chart. The calculated dewpoint value represented by the voltage at node 147 is the noninvertinginput 149 to amplifier 153. Note that where a relative humidity sensoris used (such as could be obtained from the General Eastern InstrumentsCorporation as previously noted) the dew point temperature reading wouldbe input directly to this node 147. The inverting input 151 to amplifier153 is grounded. The 141, 143, 145 resistor network reduces the signallevel of V_(DPT), so amplifier 153 amplifies V_(DPT) back to the 0.05V/°F. scaling. The V_(DPT) value passes through contacts 156 and becomesthe inverting input 161 to power amplifier 165. The cooling systemtemperature comprise the noninverting input 163 to amplifier 165 asfollows: The system temperature taken at the coolant supply manifold 21is scaled from 0 volts to 5 volts for 0° F. to 100° F. and then inputvia conductor 65 to circuitry 61 as the noninverting input 171 to poweramplifier 175. The cooling system temperature value is amplified byamplifier 175 and comprises the noninverting input 163 to amplifier 165.Amplifier 165 subtracts the dew point temperature value on pin 161 fromthe system temperature value on pin 165 to determine a temperaturedifferential value which is amplified by amplifier 165 and multiplied by10 due to the paired 10K and 100K resistors 166, 167 and 168, 169. Thegain of 10 of amplifier 165 increases the scaling of the signal at node183 form 0.05 volts/°F. to 0.5 volts/°F., or 2°F./volt. This scaledtemperature differential value is then input on the inverting input 191of comparator 195. The noninverting input 193 is a plus 2.5 voltreference level, or 5° F. on the 2° F./volt scale. Comparator 195 has alow output whenever the temperature differential value on pin 191exceeds the 2.5 volt signal on pin 193. This is a first type errorsignal. Conversely, comparator 195 has a high output 197 whenever thetemperature differential value on pin 191 is below the 2.5 voltreference. This is a second type error signal. Where the temperaturedifferential is greater than the 2.5 volt reference, the low outputproduced by the comparator 195 is inverted by NAND gate 201 to become anenabling high input to the chill NAND gate 211. Where the differentialtemperature value is below the 2.5 volt reference, the high outputproduced by comparator 195 comprises an enabling high input 245 to theheat NAND gate 251.

As shown in FIG. 3, there are two optional inputs to NAND 211 which mustbe high before NAND 211 is fully enabled to energize the motor controlcircuit to drive the mixing valve in the open direction.

The first of these is input 205. Input 205 is high when the systemtemperature exceeds the minimum temperature set by potentionmeter 215 asfollows: Potentionmeter 215 has a degrees F calibrated scale so that theuser can set a temperature (at a dial not shown) which will then bescaled to the appropriate voltage for the circuit. The temperature valueset at potentionmeter 215 is amplified at amplifier 217 and input on theinverting input 221 to comparator 225. The noninverting input 223comprises the cooling system temperature value produced by amplifier175. Comparator 225 compares the minimum temperature setting 221 withthe system temperature 223 and if the system temperature exceeds theminimum temperature, a high is output from comparator 225 to enablechill NAND input 205. If, however, the minimum temperature exceeds thesystem temperature, then the output of comparator 225 will go low todisable the chill NAND 211. Hence, input 205 ensures that the systemtemperature remains above a minimum temperature which can be set atpotentionmeter 215.

Input 207 comprises the final enabling input to chill NAND 211. Input207 comprises one output of the system dampening circuit, the otherdampening circuit output 247 goes to the heat NAND 251. Capacitor 231and resistor 232 set up the timing for the dampening circuit. In thepreferred embodiment we have chosen a 10K resistor and 50 microforad (orgreater) capacitor to achieve a suitable discharge rate for capacitor231. As long as the capacitor is discharged, the output 207 ofcomparator 243 and output 247 of comparator 241 remain high to enabletheir respective NAND GATES 211, 251. The positive side of capacitor 231is connected to a wiper arm 261 which moves with the mixing valve motorshaft. The wiper arm moves from ground potential to plus 12 volts onpotentionmeter 263 as the valve moves from its fully closed to its fullyopened position. Assuming that we start with the valve fully opened, thewiper starts at ground and the positive side of capacitor 231 would alsobe at ground potential. We assume that the negative side of capacitor231 has discharged through resistor 232 to ground. As the motor turns toclose the valve, the wiper 261 moves towards plus 12 volts and capacitor231 begins to charge. Once the negative side of capacitor 231 hascharged from 0 volts to above 0.1 volts, inverting pin 237 to comparator241 also goes to above 0.1 volts. With pin 237 above 0.1 volts, it ishigher than the positive 0.1 volt reference applied to noninverting pin233 and the output 247 of capacitor 241 goes low to disable the heatNAND 251. The positive 0.1 volt reference is supplied by the 119K.1Kresistor divider network between the +12 volt reference and ground. OnceNAND 251 is disabled the motor control circuitry (later described) isalso disabled and the motor shuts down. With the motor shut down, thepositive side of capacitor 231 remains at a fixed voltage point ofpotentionmeter 263 and the negative side discharges to ground inaccordance with the discharge rate set up by capacitor 231 and resistor232. Once capacitor 231 has discharged, the output of capacitor 241again goes high to enable heat NAND gate 251. Note that with pin 241high, common pin 235 is high also, so that the output of amplifier 243goes high to enable chill NAND 211. Since we are in a heating node,however, input 203 to NAND 211 will be disabled.

If we assume that the motor is opening the valve, and that the wiper 251starts at 10 volts, as the valve opens and the wiper arm moves towardsground, the capacitor will again begin to charge. Once the negative sideof the capacitor goes more than 0.1 volts negative, noninverting input235 will become more negative than the minus 0.1 volt reference ofinverting input 239 and the output 207 of comparator 235 will go lowdisabling chill NAND gate 211. The minus 0.1 volt reference is suppliedto pin 239 by the 119K:1K voltage divider network set up between the -12volt reference and ground. With the motor stopped, capacitor 231 willdischarge causing the output 207 of comparator 243 to go high again tore-enable NAND gate 211.

Hence, the dampening circuitry just described, by virture principally oftiming capacitor 231, damps the motion of the valve causing it to openor close in small steps. In this way, motor 13 is prevented fromovershooting and continually hunting for the 5° F. plus dew pointreference value.

Assuming then that the three inputs 203, 205, and 207, to NAND 211 areenabled, the output of NAND 211 goes low to provide a base current totransistor 277 to turn it "on". Transistor 277 in turn applies a basecurrent to transistor 281 to turn "it on" and transistor 281 in responseprovides an enabling current to the GATE 287 of triac 285 to turn thetriac 285 "on". With triac 285 turned "on" current is provided to mixingvalve motor 13 to drive the mixing valve 17 in the open direction.

Likewise, when both inputs 245 and 247 to heat NAND 251 are high, itsoutput 291 goes low which turns on transistors 295, 299, which in turnsupply current to gate 301, switching triac 305 "on" to activate themotor 13 to drive mixing valve 17 in the closed direction.

As explained previously, the valve will continue to open for so long asall the three inputs 203, 205 and 207 to gate 211 are enabled. Likewisethe valve will continue to close for so long as both inputs 245 and 207to gate 251 are enabled.

Throughout the foregoing description of FIG. 3 switches S1 and S2 hadbeen rotated counterclockwise to their automatic position to closecontacts 156 and 186. The operation of the circuit diagram of FIG. 3will now be described with switches S1 and S2 rotated clockwise to themanual position wherein contacts 157 and 187 are closed.

By closing contacts 157, the temperature value set at potentionmeter 215passes through amplifier 217 and is input on inverting pin 161 ofamplifier 165. The system temperature value 65 is amplified at amplifier175 and present at noninverting pin 163. Amplifier 165 compares thetemperature values set at potentionmeter 215 with the system temperaturevalue and outputs the difference to comparator 195 on inverting pin 191.This differential value output by amplifier 165 is scaled to 2° F./volt.Since switch S2 is now in the manual position wherein contacts 186 areclosed, noninverting pin 193 of comparator 195 is grounded. Hence, thetemperature differential value generated by amplifier 165 is compared toground potential. If it is more positive than ground potential (whichwould indicate that the system temperature is above the potentionmetertemperature setting) than the output of comparator 197 will be low whichwill enable input 203 to chill NAND gate 211 to reduce systemtemperature. If, on the other hand, the differential value on pin 191 ismore negative than ground potential (indicating that the systemtemperature is below the potentionmeter setting) than the output ofcomparator 195 will be high and will enable the heat NAND gate 251 toincrease the system temperature to bring in line with the temperatureset at the potentionmeter 215. Hence, whereas in the automatic modepotentionmeter 215 is used to set the minimum system temperature, in themanual mode the potentionmeter setting 215 is used to set the desiredsystem temperature.

Having described the basic structure and operation of the coolingsystem, the highly inventive condensation sensor is now described

The condensation sensor 335 is shown in FIGS. 4 and 5. As shown in FIG.4, the sensor 335 is mounted on a coolant system pipe 337 by means of abracket 339 which is secured to the pipe 337. Sensor 335 has a housing343 having an oblong slot 345. A bolt 347 extends through slot 345 frombracket 339 to secure housing 343 to the bracket 339. The bolt 347 canbe loosened to adjust the sensor housing 343 vertically. Pipe 337 iscovered by a layer of reflective tape 341. A light source 349 (herein anLED) is supported in housing 343 and projects light towards thereflective surface 341. Housing 343 also includes a light sensingelement 351 (here a phototransistor) which receives the light from theLED 349 reflected off of surface 341 at the point of reflection 368.Note that reflective object sensors having housings supporting a LED anda phototransistor and designed to be used in conjunction with reflectivesurfaces for various purposes are available from Altron, Inc. inCarrollton, Texas. LED 349 is disposed to project light at an angle 371with respect to vertical axis 369 which is perpendicular to reflectivesurface 341 at the point of reflection 368. Transistor 351 is disposedat an angle 373 with respect to this axis 369. The sensor 335 isgeometrically configured so that angle 371 equals angle 373. Bolt 347can be loosened to adjust the housing 343 vertically to achieve therequired distance D between the bottom 344 of housing of 343 and the top342 of pipe 337 so that angle 371 equals angle 373 and the light emittedby LED 349 is fully reflected by surface 341 to phototransistor 351 indry conditions. Should condensation begin to form upon pipe 337 at thepoint of reflection 368, then the reflection of light from LED 349 willbe impeded and the light will only be partially reflected tophototransistor 351. Circuitry associated with phototransistor 351monitors the output of phototransistor 351 and thus distinguishesbetween fully reflected and partially reflected light. This circuitry isshown in FIG. 5. As shown in FIG. 5, a current limiting resistor 353limits the current to LED 349 while variable resistor 355 is adjusted tolinearize the output of phototransistor 351 under varying lightconditions. Current output sensing device 357 measures the output ofphototransistor 351. When the light from LED 349 is being fullyreflected to phototransistor 351, device 357 measures a full scalereading. Once condensation begins to form at reflection point 348 ofpipe 337, however, reflection of the light to phototransistor 351 isimpeded and its output as measured by device 357 drops. In response tothis reduced output of the phototransistor 351, the device 357 firstshuts down the coolant pump, and then the entire computer systemcircuitry. Once the condensation evaporates, the system can either bemanually or automatically started. Note that in the presently preferredembodiment the condensation sensor 335 would be installed on one of thecoldest pipes of the coolant system, probably the coolant supplymanifold 21, in that this would be the first place where condensationwould be likely to form.

Having described the presently preferred embodiment of the coolingsystem and condensation sensor, many modifications and variationsthereof will be obvious to those skilled in the art, and accordingly,the invention is intended to be limited only by the scope of theappended claims.

We claim:
 1. In a cooling system for a computer installed in anenvironment, said cooling system including cooling conduits and coolantflowing through said cooling conduits to cool said computer, saidcooling system further including a means for controlling the temperatureof said coolant, an improvement, comprising:a means for estimating thedew point of said environment; a means for sensing the temperature ofsaid cooling system; a means for comparing said estimated dew pointtemperature with said cooling system temperature to determine atemperature differential; and circuit means responsive to saidtemperature differential for controlling said temperature control meansto maintain said cooling system temperature above said dew pointtemperature.
 2. The cooling system of claim 1 wherein said coolingsystem further includes an error generating means for comparing saidtemperature differential with a reference value to generate a first typeerror signal whenever said temperature differential is greater than saidreference value, and a second type of error signal whenever saidtemperature differential is less than said reference value, said circuitmeans being responsive to said first type of error signal to adjust saidtemperature control means to decrease said cooling system temperature,and responsive to said second type of error signal to adjust saidtemperature control means to increase said cooling system temperature,whereby said cooling system temperature is maintained one or moredegrees above said dew point.
 3. The cooling system of claim 2 whereinsaid coolant is supplied to said computer from a mixing valve through acoolant supply conduit and returns to said mixing valve from saidcomputer through a coolant return conduit having a first branchcontaining hot return coolant and a second branch including a chillerintermediate said computer and said mixing valve and containing chilledreturned coolant, said mixing valve mixing said hot return coolant fromsaid first branch with said chilled return coolant from said secondbranch to comprise said coolant flowing to said computer through saidsupply conduit, said temperature control means comprising said mixingvalve and a means for controlling said mixing valves in response to saidfirst and second error signals to drive said mixing valve in the opendirection to mix in more chilled returned coolant in response to saidfirst type error signal and to drive said mixing valve in the closeddirection to mix in less chilled returned coolant in response to saidsecond type error signal.
 4. The cooling system of claim 3, wherein saidcomputer is comprised of sections and said supply conduit feeds into acoolant supply manifold which distributes said coolant to said computersections, further including means associated with said coolant supplymanifold for determining said coolant system temperature.
 5. The coolingsystem of claim 4 wherein said dew point estimating means includes arelative humidity sensor and a room temperature sensor and dew pointestimating circuitry, said relative humidity sensor generating arelative humidity value representative of the relative humidity of saidenvironment, said room temperature sensor generating a room temperaturevalue representative of the temperature of said environment, saidrelative humidity value and said room temperature value being input tosaid dew point estimating circuitry to calculate said estimated dewpoint value.
 6. The cooling system of claim 4 wherein said dew pointtemperature T_(DP) in °F. is estimated according to the formula:

    T.sub.DP T+(RH-90)/2.4;

where "T" is said room temperature value in °F. and "RH" is saidrelative humidity value.
 7. The cooling system of claim 1 furtherncluding a condensation sensor, said condensation sensor sensing thepresence of condensation in said environment and shutting said coolingsystem in said computer in response thereto.
 8. The cooIing system ofclaim 7, wherein said condensation sensor includes a light source, areflective surface, and a light sensing means, said light sourcedirecting light at said reflective surface, said reflective surfacefully reflecting light to said light sensing means in dry conditions,and only partially reflecting light to said light sensing means in wetconditions wherein condensation has formed on said reflective surface,said light sensing means including circuitry associated therewith todistinguish between said fully reflected light and said partiallyreflected light and shutting down said cooling system in response tosaid partially reflected light.
 9. The cooling system of claim 8,wherein said reflective surface comprises reflective tape applied to aconduit of said cooling system.
 10. The cooling system of claim 9,wherein said light source comprises a light emitting diode and saidlight sensing means comprises a phototransistor.
 11. The cooling systemof claim 2, wherein said first and second type error signals are inputto motor control circuitry, said motor control circuitry enabling chilllogic circuitry in response to said first type error signal, andenabling heat logic circuitry in response to said second type errorsignal, said chill logic circuitry driving said mixing valve motor inthe open direction when enabled, said heat logic circuitry driving saidmixing valve in the closed direction when enabled.
 12. The coolingsystem of claim 11, wherein a timing means having a timing capacitor isassociated with said mixing valve motor, said timing means temporarilydisabling said chill logic circuitry or said heat logic circuitry aftersaid motor has been continuously turning in the open direction or closeddirection for a period of time sufficient to charge said timingcapacitor, said timing means comprising a dampening means for thesystem.
 13. The cooling system of claim 12, wherein said timingcapacitor is charged while said motor turns in the open or closeddirection, said capacitor disabling said chill logic circuitry or saidheat logic circuitry when it reaches its fully charged condition. 14.The cooling system of claim 11 further comprising a means for generatinga minimum temperature reference value and a means for comparing saidminimum temperature reference value with said system temperature, saidcomparator means generating an error signal whenever said systemtemperature is below said minimum temperature reference values saiderror signal being input to said chill logic circuitry to disable saidchill logic circuitry once said system temperature is below minimumtemperature.
 15. The cooling system of claim 11 having a manual mode andan automatic mode and means for switching between said automatic andsaid manual modes, including a means for generating a temperature valueand means for selectively comparing the temperature value with saidsystem temperature at a first comparator to generate a temperaturedifferential value, said circuit means being responsive to saidtemperature differential value to control said temperature control meansto equalize said temperature value with said system temperature in saidmanual mode; in said automatic mode said temperature value comprising aminimum temperature value and being selectively compared with saidsystem temperature at a second comparator, said second comparatoroutputting an error signal whenever said system temperature is belowsaid minimum temperature value, said error signal being input to saidchill logic circuitry to disable said chill logic circuitry wheneversaid system temperature is below said minimum reference temperature.